Abstract Context.Among the 160 known exoplanets, mainly detected in large
radial-velocity surveys, only 8 have a characterization of their
actual mass and radius thanks to the two complementary methods of
detection: radial velocities and photometric transit.Aims.We started in March 2004 an exoplanet-search programme biased toward
high-metallicity stars which are more frequently host extra-solar planets.
This survey aims to detect close-in giant
planets, which are most likely to transit their host star.Methods.For this programme, high-precision radial velocities are measured with
the ELODIE fiber-fed spectrograph on the 1.93-m telescope, and
high-precision photometry is obtained with the CCD Camera on the 1.20-m
telescope, both at the Haute-Provence Observatory.Results.We report here the discovery of a new transiting hot Jupiter orbiting
the star HD 189733. The planetary nature of this object is
confirmed by the observation of both the spectroscopic and
photometric transits. The exoplanet HD 189733 b, with an orbital
period of 2.219 days, has one of the shortest orbital periods
detected by radial velocities, and presents the largest photometric
depth in the light curve (%) observed to date. We estimate
for the planet a mass of
and a radius of
. Considering that HD 189733 has the same
visual magnitude as the well known exoplanet host star HD 209458,
further ground-based and
space-based follow-up observations are very promising and will
permit a characterization of the atmosphere and exosphere of this
giant exoplanet.